Syphilis, caused by the spirochete bacterium Treponema pallidum subsp. pallidum, is a chronic bacterial infection that remains a public health concern worldwide, with an estimated 12 million new cases reported in developing nations, Eastern Europe, and the Southern United States. In the absence of appropriate antibiotic treatment, T. pallidum establishes a lifelong chronic infection that may progress to the debilitating and potentially fatal tertiary disease in approximately one third of infected individuals. Apart from the serious nature of the disease itself, a number of studies suggest syphilis infections may increase the risk of acquisition and transmission of human immunodeficiency virus. The first step in establishing a T. pallidum infection is bacterial attachment and colonization of epithelial surfaces. Consequently, a logical approach for preventing T. pallidum infection is to develop methodologies for inhibiting bacterial attachment to host cells. The studies outlined in this proposal focus upon the identification of T. pallidum adhesins involved in host cell attachment, and specifically those involved in attaching to components of the extracellular matrix (ECM). The adhesins of T. pallidum will be identified using a variety of experimental techniques, including affinity chromatography and expression library screening. Putative adhesins will be expressed in a recombinant form using heterologous expression systems. These proteins will subsequently be investigated for their involvement in host cell attachment by determining their binding potential to host cells and ECM components. Confirmed adhesins will be tested for their ability to complement the non-adherent treponeme T. phagedenis biotype Reiter, and the molecular regions of the treponemal adhesins and ECM components responsible for attachment will be identified. The T. pallidum adhesins will also be analyzed for their immunoprotective potential in rabbit immunization and challenge experiments, and specifically for their ability to prevent treponemal infection. The long-term objective of the studies outlined in this proposal is to identify T. pallidum ECM-adhesins, which will in turn help to further our under-standing of the molecules involved in T. pallidum pathogenesis and identify potential syphilis vaccine candidates.